The traditional type of rigid packet, which is substantially in the shape of a parallelepiped with a rectangular cross section and sharp longitudinal corners, has some drawbacks deriving from its not very anatomic shape, which is not very pleasant to grip, and due to the fact that the above-mentioned longitudinal corners can cause wear to the pockets of the users clothing.
To overcome these types of drawbacks the prior art proposes numerous types of packets having rounded corners or even a substantially elliptical or oval cross section.
For example, the document WO-A-0144077 in the name of the same Applicant as this invention, shows a rigid packet for cigarettes, of the hinged-lid type, having all the longitudinal corners (that is, parallel to a main direction of the packet) rounded, with concavity facing the inside of the packet, in such a way as to eliminate the presence of sharp corners.
This solution, even though it allows the wear of the users clothing to be limited, does not significantly improve the grippability of the packet.
Moreover, it has been found that the absence of sharp longitudinal corners causes a poor structural rigidity resulting in an easy deformability of the packet, especially at the rounded corners.
A further drawback is that the rounded corners can only be achieved with major modifications to the traditional machines for packaging. More specifically, it was necessary to perform complex steps of pre-deforming areas of the blanks that will constitute the strips defining, upon completing the packet, the rounded corners.
Another prior art solution, free from most of the drawbacks mentioned above, is known from the patent publication ITBO98A000008, again in the name of the same Applicant as this invention, which illustrates a packet for cigarettes, of the hinged-lid type, wherein at the longitudinal corners there are connecting walls having a same variable dimension along the main direction of the packet.
In this way, the perimeter extension of the packet has a maximum value and a minimum value, at a gripping area.
In other words, the connecting walls with variable dimensions allow the cross section of the packet to be reduced in at least one predetermined area thereby facilitating the gripping.
Disadvantageously, this solution has been found to be problematic in the steps of wrapping the packet.
In effect, the traditional cellophaning machines, designed to wrap the packets with a transparent outer wrapping sheet, provided for parallelepiped packets with sharp longitudinal corners, have been found to be unsuitable for that operation on those types of packets.
More specifically, in the area with a minimum cross section it becomes difficult to perform a correct wrapping of the packet and spaces are created with consequent formation of unattractive creases and folds.